VAEIABLE RESEMBLANCE IN VERTEBRATA, ETC. 99 



the formation of gas bubbles. The many recorded 

 cases of hair turning white in a few hours as the 

 result of some strong nervous shock are to be explained 

 in the same manner. . 



That the change in the long autumnal hairs of 

 Lepus Americanus is due to the appearance of large 

 numbers of bubbles is rendered probable by an exami- 

 nation of Welch's figures and descriptions. He speaks 

 of the white part of a hair being much broader than 

 the coloured part, and containing additional rows of 

 'cells.' His 'cells' appear to be bubbles of gas, 

 and he draws them with the characteristic dark 

 borders. It must be remembered that the dark parts 

 of a hair also contain bubbles, although in smaller 

 amount. 



The change in the hair is indirectly caused by the 

 change of temperature 



It is extremely improbable (to say the least) that 

 such changes as the evolution of bubbles, and above 

 all, the growth in length, are the direct result of a 

 lowered temperature on the hair itself. That they 

 are indirect results, through the nervous system, is in 

 every way probable, and is furthermore in harmony 

 with certain well-known facts concerning the regula- 

 tion of temperature. 



The direct tendency of cold is clearly to diminish 

 the activity of those processes upon which the pro- 



